The Three Lights, an idol rock band, appear in Tokyo at the same time as the Animamates. Their true identities are the SailorStarlights, Sailor Senshi from a different galaxy. Their goal is to find their Princess.

Mamoru leaves to Harvard for a year or so in a plane, but it turns out that while in flight, Galaxia came and took his star seed. In the meantime in Tokyo, Chibi-usa has gone home to the future, and in her stead, Chibichibi arrives, posing as Usagi's little sister after brainwashing Usagi's mom. She has the chalice, which she uses to help Princess Kakyuu come to Earth. She also gives Eternal Sailormoon her new power-up and is revealed to be a senshi.

Most of SailorStars focuses on the Three Lights interacting with the Sailor Senshi and the search for the star seeds. Seiya has a crush on Usagi, but Usagi does not feel the same. The Outer Senshi are extremely hostile to the Starlights because they feel they do not belong on Earth. Eventually the Starlights find their princess, Princess Kakyuu, who saves Usagi and ChibiChibi from Tin Nyanko. However, she is soon killed by Galaxia after her star seed is extracted from her.

The Inner Senshi and the Starlights confront Galaxia, but Galaxia merely kills off the Inners, taking their star seeds as well. She then starts to do massive star seed collecting all over Tokyo, taking any and every one from all the people. The Outer Senshi go by themselves to fight Galaxia, but they are also ineffective. Uranus and Neptune then agree to give up their star seeds to work under Galaxia, killing Pluto and Saturn to prove their loyalty. They also attack the Starlights and Sailormoon, but when given their final order to destroy their former allies, Uranus and Neptune turn on Galaxia, trying to take her star seed. Since Galaxia doesn't have a star seed, this doesn't do much, and she kills them instead.

Sailormoon, Chibichibi, and the Starlights are left, and actually the Starlights do pretty little in the battle except to protect Sailormoon. Chibichibi finally reveals her nature- she is the hope of Galaxia's star seed who was released when Chaos entered Galaxia's body, turning her evil. ChibiChibi transforms into a sword for Sailormoon/Princess Serenity to destroy Galaxia, but Sailormoon refuses to use it. Sailormoon finally wins the battle by reaching towards the goodness left inside of Galaxia, and Galaxia becomes good again once Chao leaves her body. She releases all the star seeds, and then she leaves. The other Sailor Senshi, Kakyuu, and Mamoru return to life, and then the Starlights leave with their princess as life returns to normal at the end of the series.